Air quality

Review and Assessment of PM10 Particles

Information about air quality in solihull

8 Review and Assessment of PM₁₀ Particles

8.1 The Government

has adopted two air quality standards for PM₁₀ particles:-

A fixed 24-hour mean of 50µg/m³, with the objective that it may be exceeded no more than 35 times per year by the end of 2004 (approximately equivalent to the 90^th percentile of the total annual daily values).

An annual mean of 40µg/m³, with the objective of meeting that standard by the end of 2004.

For both objectives, the focus of the review and assessment should be on non-occupational exposures at near ground level outdoor locations, where the public may be exposed for any substantial part of the day, including:-

• Background locations,
• Roadside locations, close to the facades of buildings,
• Other locations where people may be regularly exposed, such as in the vicinity of housing, schools or hospitals.

8.2 Unlike the individual gaseous pollutants

discussed elsewhere in this report, which are single, well-defined chemical substances, particulate matter in the atmosphere is composed of a wide range of materials arising from a variety of sources. These can be classified into three main categories:-

• Primary combustion particles 0 these are particles emitted directly from combustion processes such as motor vehicle engines, power generation boilers and industrial and commercial combustion plant. Primary combustion particles are generally much less than 1µm in diameter.
• Secondary particles - these are particles formed by chemical reactions in the atmosphere. They include nitrates and sulphates formed by the oxidation of nitrogen dioxide and sulphur dioxide. Secondary particles are generally less than 2.5µm in diameter.
• Coarse particles- these generally arise from non-combustion sources, such as resuspended dust from construction work, mineral extraction processes and road traffic, and wind blown dust, soil and sea salt. These particles are generally larger than 2.5µm in diameter.

8.3 It is important to identify the sources of each category of particles

and their contributions to the PM₁₀ concentrations, because the expected reduction in particle emissions is different for each type of particle. For example, the emissions of primary combustion particles from road transport will be affected by legislation on vehicle emission standards, whilst the emissions of secondary particles will be affected more by controls on large combustion plant and the emissions of nitrogen dioxide and sulphur dioxide. Emissions of coarse particles are largely uncontrolled and so are unlikely to change.

8.4 The main sources of PM₁₀ particles

for non-occupational exposures, are emissions arising from the combustion of fossil fuels in road transport, power stations and other industrial and commercial activities, the formation of nitrates and sulphates in the atmosphere and resuspension of surface dust and soil.

8.5 Specific sources of PM₁₀ particles in Solihull are:

• Emissions from motor vehicles,
• Emissions from industrial combustion plant,
• Emissions from commercial combustion plant,
• Long range transport of secondary particles.

Sources of PM10 Particles in the West Midlands

Figure 8.1

8.6 Levels of PM₁₀ Particles in 1999

Air pollution is measured at a number of locations across the West Midlands conurbation. Some of the monitoring stations are owned and operated by the Government, as part of the Automatic Urban and Rural Network (AURN). Others are owned by Local Authorities, but are affiliated to the AURN. Also included is a monitoring station at Birmingham Airport. In this report, the levels of PM₁₀ particles, measured at AURN stations in neighbouring authorities, are included to demonstrate the relationship between the levels, across the conurbation.

It is suspected that the TEOM method, used in the United Kingdom to measure PM₁₀ particles, underestimates the levels of those particles because the technique involves heating the samples to eliminate the effect of moisture in the atmosphere. Unfortunately this practise is thought to cause a loss of some volatile pollutants. So, the Government recommends that TEOM measurements are corrected for the loss of volatile material, for assessment against the Air Quality Standard. The current recommendation is to multiple the TEOM values by a factor of 1.3. The values presented in Figures 8.2 to 8.5, inclusive, have been corrected by this factor.

As Figure 8.2 shows, the first of the Air Quality Standards 2000 for PM₁₀ particles; 50µg/m³, expressed as the 35^th highest daily concentration, was met at each of the region's monitoring stations, in 1999.

35th Highest Daily Values in the West Midlands PM10 Particles, 1999

Figure 8.2

Similarly, Figure 8.3 shows that the other Air Quality Standard 2000 for PM₁₀ particles; 40µg/m³, expressed as the annual average concentration, was also met at each of the region's monitoring stations.

Annual Average Values in the West Midlands PM10 Particles, 1999

Figure 8.3

Solihull MBC has a mobile air quality station that has been in operation since 27th April 2000. It has been located at two urban background sites: Coppice Junior School (off Damson Lane) from 27th April 2000 to 15th October 2000, and Marston Green Infants' School from 30th October 2000. Figures 8.4 and 8.5 show the monthly averages and the 35th highest hourly mean respectively for PM₁₀ as recorded at the station.

PM10 Monthly Averages May 2000 - Mar 2001 (TOEM - corrected)

Figure 8.4

PM10 35th Highest Daily Values (TOEM - corrected)

Figure 8.5

The trends in the maximum and annual average concentrations for PM₁₀ particles are shown in figures 8.6 and 8.7, respectively. Both have shown a progressive improvement throughout the 1990s. Although the concentrations of air pollutants vary from year to year, due to varying weather patterns, the overall levels of pollution will drop if the emissions of a pollutant are falling. Thus, as the vehicle fleet changes, due to the introduction of new vehicles with lower emissions and the removal of older vehicles with higher emissions, less of primary PM₁₀ is emitted, less secondary PM₁₀ is formed locally and hence the air quality improves.

Trends in West Midlands Air Quality PM10 Particles: 35th Highest Daily Value

Figure 8.6

Trends in West Midlands Air Quality PM10 Particles: Annual Average Values

Figure 8.7

8.7 Future Trends in the Levels of PM₁₀ Particles

The change in concentrations of PM₁₀ particles in the atmosphere, over the next five years, will depend on three factors:-

1. the amount of fine particles emitted from primary combustion processes, locally;

2. the quantity of secondary particles formed in the atmosphere and carried into the City from sources elsewhere in the region, the country or even Europe;

3. the amount of dust resuspended, locally, from road surfaces by vehicles and by the action of wind on soil and surface dust and stockpiles of dusty materials.

The Government's guidance to local authorities, LAQM TG4 (00), provides a method to calculate the probable concentrations of PM₁₀ particles in 2004. The calculations indicate that the 35^th highest daily value is likely to be 39µg/m³ and the average urban background is likely to be 22µg/m³.

Alternatively, the future concentrations may be calculated by applying the projected changes in emissions, between the present time and 2004, to the trend in measured values for the area. The results of such a calculation are presented in Figures 8.8 and 8.9. The figures show that 35^th highest daily value and annual average are expected to be 30µg/m³ and 21µg/m³, respectively.

Trends in West Midlands Air Quality PM10 Particles: 35th Highest Daily Value

Figure 8.8

The two methods of calculation show good agreement for the annual average values, but poorer agreement for the highest daily values. Calculating the future values from the changes in local emissions does not take adequate account of transport of secondary particles into the area.

Trends in West Midlands Air Quality PM10 Particles: Annual Average Values

Figure 8.9

Both methods of estimating future concentrations suggest that the air quality objective for 2004 should be met at urban background sites within the Borough.

8.8 Changes to the Air Quality Standard and Objective for PM₁₀ Particles

When the Stage 1 Report on Sources on Air Pollution in Solihull was prepared the Air Quality Regulations 1997 were the relevant regulations. These laid down a standard for PM₁₀ particles of 50µg/m³, when expressed as the 99^th percentile of the maximum running 24-hour averages. This is equivalent to meeting this standard on all but four days per year.

The Air Quality Strategy has since been revised by the Government, and the Air Quality Regulations 1997 have been superseded by the Air Quality Regulations 2000. The latter now set a standard for PM₁₀ particles of 50µg/m³, when expressed as maximum daily values, and with a new objective that the standard should not be exceeded more than 35 times per year. The target date for meeting the new objective is 2004. This represents a considerable relaxation to the objective.

As figures 8.6 and 8.8, above, demonstrate, the new objective has been achieved throughout the West Midlands since 1997. Furthermore, since the trend in the 35-highest daily values is downwards, it appears likely that the objective will still be met in Solihull in 2004.

Computer modelling, which has been undertaken to date, has revealed that industrial emissions of PM₁₀ particles are poorly quantified, and that estimates of secondary particle formation and resuspension of surface dust are not accurate enough for urban pollution modelling.

Studies are now underway, in the West Midlands, to measure PM₁₀ particles at a number of roadside locations, and to make comparative measurements of PM₁₀ and PM_2.5 particles, by both the TEOM and gravimetric techniques, and to count airborne particles.

The outcome of these studies and of more accurate estimates of the emissions of PM₁₀ particles from industry, will be considered in more detail in the next round of review and assessment, to be completed in 2003.